The Cost of Obesity
Commentary on an article by Hilal Maradit Kremers, MD, MSc, et al. “The Effect of Obesity on Direct Medical Costs in Total Knee Arthroplasty”
Stephen J. Incavo, MD; Aditya M. Derasari, MD


Obesity is associated with longer hospital stays and increased costs in total knee arthroplasty, even among patients without comorbid conditions or complications. Every 5-unit increase of body mass index (BMI) over 30 kg/m2 is associated with increased costs of $250 to $300 for primary total knee arthroplasty and $600 to $650 for revision total knee arthroplasty. This is the important conclusion that the authors have demonstrated in their article. We stress that this is an important conclusion for several reasons.

First, the negative consequences of obesity regarding disability, disease, and mortality have been well documented, and, unfortunately, obesity is increasing in the United States. Obesity is linked to degenerative arthritis of the knee, and a substantial number of patients undergoing total knee arthroplasty are obese1. Although others have reported this, the results of this study indicate that 59% of patients undergoing primary total knee arthroplasty and 62% of patients undergoing revision total knee arthroplasty are obese.

Second, improvement in outcomes following total knee arthroplasty in obese patients has been reported; however, previous studies have been less definitive regarding the role of obesity contributing to higher costs in patients undergoing total knee arthroplasty2. The detailed analysis and robust costing methodology used in this study provide more current and compelling data to demonstrate the increased costs incurred by these patients. As obesity is an associated risk factor with many comorbidities and complications following total knee arthroplasty, it has been difficult to properly attribute increased costs to any one factor. The authors of this study examined the direct medical costs and length of hospital stay of total knee arthroplasty in obese patients taking into account comorbidities and complications. They found higher length of stay and direct medical costs in obese patients. Notably, these findings persisted when adjusting for comorbidities and complications.

Third, in the climate of limited financial resources and increasing scrutiny, it is imperative to identify sources of increased cost and burden to the health-care system. This well-constructed study adds to our existing knowledge on total knee arthroplasty in obese patients. Complication rates, particularly wound infection and increased operative times, are seen in obese patients who undergo total knee arthroplasty3. This is true of this study as well, which demonstrated higher infectious complications in obese patients. Total knee arthroplasty in obese patients is effective but fraught with complications: 7% of patients who underwent primary total knee arthroplasty and 9% of patients who underwent revision total knee arthroplasty in this study had complications. It follows that sicker obese patients prone to complications are more costly to treat. This study goes further and concludes that obesity on its own confers significant costs to the health-care system. Although individual cost components were not included in the analysis, the authors suggest that room and board and increased operating room time contributed to the majority of the increased costs. Reducing these parameters may confer some cost savings or, more likely, simply cost shifting. As mentioned in the study, the costs to skilled nursing facilities, to which many obese patients were discharged, were not calculated.

One important question that the authors do not address is: Who pays for the increased costs? Several different groups bear most of the burden: the health-care system (or perhaps society in general), which will see increased costs for earlier revision surgery either for infection or mechanical complications; rehabilitation or skilled nursing facilities, which will see an increased use; and employed family members, who will require more out-of-work days to provide home support.

Although difficult to quantify, hospitals, which often rely on a fixed payment, need extra personnel and equipment to lift and to transport morbidly obese patients. Work-related disability may be affected from the heavy lifting of patients. Finally, surgeons and other providers will be required to provide more care with the same reimbursement. Longer surgical times and complexity are obvious unreimbursed problems. More frequent inpatient and outpatient calls for medical and surgical management issues certainly exist. Relatively poorly reimbursed revision surgery will inevitably be a larger surgical burden. Noticeably absent from the list of who pays are the obese patients themselves.

In summary, total knee arthroplasty is a more costly enterprise in an obese patient. These costs cannot be mitigated by adjusting for comorbidities or postoperative complications. Even a relatively “healthy” obese patient who undergoes uncomplicated total knee arthroplasty confers an increased financial burden to our health-care system.


  • * None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.


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